Disinfection of water on-board passenger transportation vehicles is necessary to guarantee water quality. This may include disinfection of potable water that is held in a self-contained potable water tank onboard the vehicle. The water held in the tank is ultimately intended for delivery to beverage makers, sinks for hand-washing, toilets for flushing, or is otherwise routed on-board the vehicle for various forms of use or consumption such as humidifier. As one example, water systems on aircraft are complicated systems that usually include a tank with plumbing conduits and a pressurization system to deliver water to the various points of use.
The issue of water quality, and in particular, of potable water quality, on passenger transportation vehicles and equipment, such as aircraft, trains, boats and ships, and the like is a point of interest for regulatory authorities. Regulatory standards have been enacted that require water carried on-board passenger vehicles to meet certain standards such as the US EPA Aircraft Drinking Water Rule. Passenger airlines and other transportation companies must thus meet the relevant drinking water standard. If failing to do so, the aircraft water system has to go through disinfection process per specified protocol and retested, accordingly. This can lead to the aircraft being grounded until retesting of water quality and confirmation that the water management system is free of any microbial contamination.
Airlines and other passenger transport vehicle companies must ensure that the potable water (i.e., drinkable water) carried aboard the aircraft is fit for human consumption by employing appropriate disinfection protocols and prevent cross-contamination during water upload. Disinfection upon upload and periodic disinfection sampling does not always adequately address the issue of contamination that may occur in the water tank and/or when the water is leaving the tank for use on board the aircraft. For example, air must periodically be introduced into the water storage and dispensing system on the aircraft in order to maintain pressurization, as well as to drain the system during routine servicing. This air can introduce airborne pathogens or bacteria that can multiply and cause unsanitary conditions and unacceptable water quality in the intervals between samplings or disinfection procedures. In effect, because the water storage and dispensing system is routinely exposed to the outside environment, potable water quality inside the water holding tank cannot always be ensured without some form of additional treatment. Additionally, water storage tanks are often drained at the end of the flight in order to prevent water freezing or other bacterial buildup. Because the internal surface of the water supply tank is then subjected to moist air from many hours until the surface dries, this can also be a breeding ground for microorganisms or other biofilms.
Specifically, microorganisms and biofilms may contaminate water held in a self-contained potable water supply, such as water tanks located onboard passenger transportation vehicles. Accumulation may occur along the interior surfaces of the water tank. It is also possible for bacteria, viruses, spores, mold, algae, or other microorganisms to grow in contaminated water holding tanks. The moist metal or plastic interior surfaces of the water tank in a light absence setting may provide a prime breeding area for microorganism biofilms that may build up and slough off into the water. There is thus a need to further disinfect the water that is held in the water tank on an on-going basis, not only upon upload or its delivery to its point of use.
Chlorination or other chemical treatment is not always effective in reducing or removing bacteria lying beneath a protective biofilm. On the other hand, ultraviolet (UV) light treatment can eliminate bacteria, viruses, spores, and mold in the water. It can purify water by making biological impurities inactive. Ultraviolet lamps are generally designed to destroy the links in these micro-organisms' DNA so that they are de-activated and cannot reproduce. The crucial hydrogen bonds that link the DNA chain together rupture when exposed to light between the wavelengths of about 220 nm to about 310 nm. In a particular example, the range may be from about 250-270 nm. In an even more particular example, there may be a single mono wavelength of 254 nm.
There are a number of water treatment solutions being employed and/or studied for use on-board aircraft. For example, one way that water can be treated is via UV mercury lamps. These lamps deliver an ultraviolet light to the water in the system and have been found beneficial because the treatment does not change the taste or odor of the water, it kills bacteria, viruses and protozoan, it is compact and easy to use, and it can prevent biofilm if the system is kept clean. However, one of the disadvantages of mercury UV lamps for water treatment is that they require a medium to high electrical demand, which means that when used on-board a vehicle such as an aircraft, they pull electrical power from the aircraft engines and/or an auxiliary power unit (APU). Increased usage of aircraft power from the engines results in higher fuel consumption and costs. Other disadvantages are that UV mercury lamps require cleaning and new lamps annually, and if a mercury lamp is broken, there exists a chance for mercury contamination of the water to be treated. Additionally, UV lamps take a while to power on if not in constant use. For UV lamps, the highest peak is generally mono-chromatic, in that the lamps generally only emit one effective wavelength, which is usually 254 nm for water treatment.
A further method of water treatment that has been explored is the use of ultraviolet light emitting diode (UV LED) light for water treatment. In addition to the mercury lamp benefits, the use of UV LED light also has the advantage of being able to use a wider UV band with multiple LED wavelengths, and it can offer a high power output with less power consumption than UV lamps. UV LEDs have greater longevity, power up quickly without requiring a delay time built into the system for the UV light source to reach its optimum UV energy output, and do not contain mercury. There are not currently available systems that are designed for use on-board a transportation vehicle such as aircraft that are imbedded and/or part of the tank water structural design.
Therefore, a current need exists for a UV LED system for use in a vehicle or aircraft environment that can deliver appropriate UV treatment to water contained and being held in an onboard potable water tank. The present assignee owns patents related to point of use water treatment (U.S. Pat. No. 9,260,323), to water treatment upon upload (U.S. Pat. No. 9,061,923), and to chemical water treatment (U.S. Pat. No. 7,666,317). However, it has been determined desirable to provide a system that can be installed within the water holding tank on board a vehicle. Some companies provide water treatment units that recirculate water from the tank through the unit, returning the water to the tank during flight. However, the problem of direct in-tank water treatment has not been adequately solved to date.